"Wo unto them that turn aside the just for a thing of naught and revile against that which is good, and say that it is of no worth! For the day shall come that the Lord God will speedily visit the inhabitants of the earth; and in that day that they are fully ripe in iniquity they shall perish. But behold, if the inhabitants of the earth shall repent of their wickedness and abominations they shall not be destroyed, saith the Lord of Hosts."
Nephi warns against "turning aside the just for a thing of naught." A "thing of naught" means something without value. To "turn aside" is to leave or move away from. So he is telling you to be careful to not walk away from the truth being taught by a "just" or true source, and instead follow after something of no value.
This rejection of a true messenger and following after a false one inevitably results in "reviling that which is good." When you reject the truth you normally have to deal with a troubled conscious. The way to calm it is to "revile against" the thing you have rejected. Not only do people "revile against" the message, but they go on to "say that it is of no worth!"
Think about the general reception given to the Lord's messengers throughout scripture. They are always the object of criticism and reviling. Nephi is describing a syndrome here which always attaches to the true message and true messenger. They aren't valued, but thought "a thing of naught." The argument is always: "If what they had to say were important, it would come from someone more important." Content is ignored in favor of status.
Now the Lord allows this to go on and always has. But, as Nephi reminds us, there does come a time when the limit has been reached. When the limit has been reached, the end "will speedily visit the inhabitants of the earth." That is, when the time has come, the turn will be so swift that they cannot repent any longer. Judgment will overtake them too quickly.
The moment when they have reached the limit is described by Nephi as "fully ripe in iniquity." That means they will no longer even listen to the truth. They have completely closed minds. It would do no good to extend them further opportunity, because they will not take any advantage of it.
So they are scheduled for destruction.
BUT, Nephi reminds us, they can repent. If they will change their minds and come to Christ, He will forgive them and heal them. If they repent, they will be preserved from the destruction. However, as has already become clear, their destruction is due to the fact they are "fully ripe." So although repentance remains theoretically possible, and the Lord will accept even late return to Him, the offenders are committed to their offense. They are not likely to take advantage of the opportunity.
How humble it is for the Lord to be willing to accept the reluctant, tardy and slow to repent. Nevertheless, He is willing to accept even them. He suffered for all, and will redeem as many as will come to Him. Initially, He won't destroy them with the wicked. Ultimately the outcome will depend upon how committed they are to the process of repentance. For to repent is to come to Him. They decide if His open arms will be where they finally embrace Him; of if they will stand afar off and think it too hard to surrender their sins and go further.